1. Field of the Invention
The present invention relates to an improvement of an ultrasonic therapy apparatus for destroying an object, e.g., cancer cells or stones, in a subject to be examined by focused energy of a shock wave, or to perform treatment.
2. Description of the Related Art
A conventional ultrasonic therapy apparatus, for example, an extracorporeal shock wave treatment apparatus, comprises an applicator, an applicator support unit, a couch for providing support to a patient, a shock wave control device, a tomographic imaging display unit, and a water control device, etc. The applicator includes a shock wave transducer which has a plurality of electro-acoustic transducer elements for transmitting a focused shock wave to a predetermined direction and depth in the patient. A transmission side of the applicator is controlled to the patient downwardly, after that, the transmitted shock wave from the shock wave transducer can effectively destroy a kidney stone or gallstone in the patient.
Consequently, in a conventional shock wave treatment apparatus, whereby the applicator is arranged above the patient, transmits the shock wave to the patient downwardly. This arrangement of the applicator is defined as a downward approach type. On the other hand, an applicator arranged below the patient transmits the shock wave to the patient upwardly. This arrangement of the applicator is defined as an upward approach type. An advantage of the upward approach type to the other type is easy operation for coinciding a focus point of the shock wave to a calculus. Namely, the operator can adjust the position of the applicator by virtue of confirmation of the positions of several parameters, e.g., condition and body surface of the patient, position of the applicator, and the contact condition between the patient and the applicator.
Although the upward approach type has the advantage of easy operation for adjusting the focus position against the calculus, the upward approach type also has disadvantages when the therapy object is a gallstone.
When a gallstone is destroyed by the shock wave from the applicator of the upward approach type, the patient lays prone. In the prone posture, the gallstone is positioned under a rib and lung. Hence, the transmitted shock wave is absorbed and attenuated by air in the lungs. And in the shock wave therapy apparatus using a ultrasonic imaging probe positioned in the center of the applicator, the structure under the lung is not displayed on the ultrasonic tomographic image, because the ultrasonic beam from the imaging probe is also absorbed and attenuated by air in the lungs. Further, the gallstone is moved by patient movement, based on breath, etc., hence the above operation for coinciding the focus to the gallstone is very difficult.
Furthermore, when the applicator using the downward approach is contacted with the patient, the distance between the applicator and a kidney stone in the patient is approximately 5 cm to 12 cm, and the distance between the applicator and the gallstone in the patient is approximately 2 cm to 7 cm. As is well known in ultrasonic technology, the attenuation coefficient of tissue varies with depth of the object. The attenuation coefficient of tissue increases substantially linearly with frequency, with the high frequency spectral components of a returned signal being attenuated more severely than the low frequency components. Typically, the center frequency of the received signal drops in frequency with the depth of penetration.
Such problem is related to the shock wave treatment apparatus in hyperthermia, with the upward approach applicator type also having the same problem.